Lymphoscintigraphic Evaluation of Systemic Tracer Uptake in Patients with Primary Lymphedema
Jeremy A. Goss, MD, Reid A. Maclellan, MD, MMSc, Arin K. Greene, MD, MMSc.
Boston Children's Hospital, Harvard Medical School, Boston, MA, USA.
BACKGROUND: Lymphoscintigraphy is used to confirm the diagnosis of lymphedema; pathological findings are abnormal transit time to regional nodes and dermal backflow. The radionuclide study involves the injection of a tracer protein (99mTc-sulfur colloid) into the distal extremity (i.e., hand or foot), after which the tracer is taken up by the lymphatic vasculature. One endpoint for the test in patients with primary lymphedema is to ensure a patent thoracic duct by uptake of tracer in the organs. The purpose of this study was to evaluate transit of radiolabeled colloid to the organs in order to gain insight into the etiopathophysiology of primary lymphedema.
METHODS: Patients treated in our Lymphedema Program between 2009 and 2017 were reviewed. Diagnosis was determined based on history, physical examination, photographs, and imaging studies. Only patients with bilateral lower extremity primary lymphedema were included (individuals with unilateral leg lymphedema were excluded because the tracer will reach the venous circulation and organs through the normal extremity). Sex, age-of-onset, location, morbidity, disease severity, and lymphoscintigraphy findings were documented.
RESULTS: Sixty-one patients were included. Ten subjects had no radiolabeled tracer transit to their inguinal lymph nodes on lymphoscintigraphy. However, 8 of these individuals had tracer uptake to the liver, kidney, and/or bladder illustrating clearance of tracer into the systemic venous circulation. All 8 patients had infant-onset primary lymphedema and mild disease. The two patients that did not have clearance of tracer to the systemic venous circulation developed lymphedema in adolescence and had clinically moderate or severe disease.
CONCLUSIONS: Patients with primary lower extremity lymphedema often have pathways for lymph fluid to reach the venous circulation other than through the inguinal nodes and thoracic duct. These patients have mild disease likely because of lymph flow through venous conduits. The limb may compensate for the paucity of lymphatic vasculature by forming lymphatic-venous connections or veins that have a lymphatic phenotype to allow the drainage of large proteins and fluid into the venous circulation.
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